And I'm Melissa Block. President Obama announced a major shift in immigration policy today. It protects many illegal immigrants who came to this country as children from being deported, at least temporarily. The president said he's taking this action on his own because Congress failed to pass a more sweeping overhaul of immigration laws. As NPR's Scott Horsley reports, the move could rally Latino voters who were a major part of Mr. Obama's winning coalition four years ago.

SCOTT HORSLEY, BYLINE: President Obama says the new policy's designed to make immigration enforcement more fair, more efficient and more just by not using the powerful weapon of deportation against those who crossed the border as children and have lived in this country for most of their lives.

PRESIDENT BARACK OBAMA: They pledge allegiance to our flag. They are Americans in their heart, in their minds, in every single way but one, one paper.

HORSLEY: The new policy applies to illegal immigrants who came to the U.S. when they were 15 or younger and have lived here continuously for at least five years. If they've gone to school or served in the military and avoided serious trouble with the law, these immigrants may be allowed to avoid deportation for two years and possibly longer. They'll also be eligible for a work permit.

OBAMA: Now, let's be clear. This is not amnesty. This is not immunity. This is not a path to citizenship. It's not a permanent fix.

HORSLEY: While the administration argues this is not a blanket policy and that cases will still be reviewed one my one, the White House says the move could help as many as 800,000 illegal immigrants. Independent estimates say the number could be even higher. That alarms Roy Beck, an outspoken critic of illegal immigration, who heads the group Numbers U.S.A.

ROY BECK: Is there anybody in America who believes that the 20 million unemployed or underemployed Americans need more competition?

HORSLEY: Latino activists, on the other hand, have been pleading with Mr. Obama to take this step, even as they wait for Congress to pass more comprehensive immigration reform. Illinois Congressman Luis Gutierrez went so far as to be arrested outside the White House while protesting the administration's inaction on immigration reform. Gutierrez says the new policy makes this a great day.

REPRESENTATIVE LUIS GUTIERREZ: I want to congratulate - no, I want to thank the president of the United States. We've had our disagreements on the extent of prosecutorial discretion and what the president can and cannot do. But as those who have always advocated for a permanent solution, I think this is just wonderful.

HORSLEY: Republican White House hopeful Mitt Romney took a hard line against illegal immigration during the primaries. Today, he said there might be some accommodation for those who came to the U.S. as children, though he criticized Mr. Obama for his unilateral action.

MITT ROMNEY: This is an important matter. We have to find a long term solution, but the president's action makes reaching a long term solution more difficult.

HORSLEY: The president was even heckled today during his Rose Garden announcement by a reporter from a conservative website. Cutting the man off, Mr. Obama curtly insisted the new policy is the right thing to do.

OBAMA: Because we are a better nation than one that expels innocent young kids.

HORSLEY: The policy could also pay political dividends for the president if it boosts turnout among Latino voters in November. Latinos were strong backers of Mr. Obama four years ago, but since then, some have grown disillusioned by the slow pace of immigration reform and the rising number of deportations. News of the policy change comes as Mr. Obama and Romney are preparing to address a major gathering of Latino politicians next week.